The present invention concerns a cooled mirror device for laser systems. Mirror devices of that kind are typically employed as reflection elements in industrial manufacturing installations using a (power) laser, for example when cutting or welding.
By virtue of a laser output power which can be in the double-digit kilowatt range, it is necessary in that situation to cool the mirror device; even mirror surfaces which are of optimum physical suitability and mechanically prepared (for example a copper surface for the wavelength of 10.6 micrometer of a CO2-laser) only achieve a reflection of 99% so that the absorbed laser power has to be removed by a cooling system connected to the cooling device.
By virtue of its favourable reflection properties, copper is a known material for the production of mirror devices of the general kind set forth; it is therefore known from the state of the art for both the mirror cover (which forms the actual mirror surface) and also the main mirror body to be formed from solid copper. That does not involve any problems and is well-established in the state of the art, in particular in regard to simple and inexpensive manufacture and repair (for example by refurbishing a worn mirror surface).
That however appears to give rise to problems precisely in relation to future, laser-based processing and machining machines which are moved by high-dynamic linear motors (at feed speeds of up to 20 m/min): the high weight of cooled mirror devices of the general kind set forth, which is caused by the high specific weight of copper, not only involves increased demands in terms of load-bearing capability and the implementation of adjusting and control devices, having regard to the high speeds involved and the correspondingly high levels of acceleration, but also the dynamic vibrational behaviour of mirror devices of that kind means that it is necessary to reckon on a reduction in the speed of working cycles which can be employed in a practical context as, after each control or setting operation, a settlement procedure (which ultimately is dependent on the weight of the mirror device) first has to be effected before the laser machining unit can be used.
A further disadvantage of known mirror devices of the general kind set forth is that the cooling devicexe2x80x94typically in the form of a duct in spiral form which is milled into the main mirror body or the mirror coverxe2x80x94is also a copper element. When water is used as the common cooling fluid, the result of this is that it is also only possible to use pure copper conduits or passages in a cooling circuit (with further mirror devices and other units), as otherwise, for example in a situation involving an aluminum cooling passage coupled into the cooling circuit, the otherwise known effect of the material being eaten away occurs due to cathodic or anodic action.
Therefore the object of the present invention is to improve a mirror device of the general kind set forth, in such a way that in particular the properties of such a mirror device are improved in connection with high-dynamic control motors in a laser system, without worsening the reflection properties, for example by virtue of another choice of material for a mirror surface, and without a substantially increased level of expenditure having to be accepted in terms of manufacture and production.
In addition a mirror device of the general kind set forth is to be the subject of further development to the effect that the cooling device can be operated not only in a cooling circuit with the same metal or the same metal alloy, without material damage occurring.
That object is attained by a mirror device having a mirror cover made of an aluminum material which is coated with a reflection-enhancing material to form a reflection-enhancing mirror surface.
In a manner which is advantageous in accordance with the invention, the present invention makes it possible to provide a mirror device which is suitable in particular also for high-power lasers within a laser system, which, by virtue of a markedly reduced weight, with positive reflection properties which are unchanged in comparison with a solid copper mirror device, is of optimum suitability for rapidly movable or rapidly accelerated units within modern manufacturing installations.
In addition the use of the aluminum material according to the invention has a favourable effect both in terms of production costs and also in regard to the dissipation of heat from the mirror surface. In this respect, the term xe2x80x98aluminum materialxe2x80x99 is to be interpreted in the context of the present invention as not only meaning solid aluminum; but rather that definition includes any aluminum-based alloys which, with a predominant proportion of aluminum in comparison to other alloy elements, permit implementation of the perceptible weight advantage in relation to copper.
In addition, according to the respective thickness of the reflection-enhancing copper layer, it is possible either to post-machine same (without renewed coating), for example by the otherwise known use of diamond turning machines with a nanometer level of resolution, or to apply a fresh copper layer, in a particularly suitable manner by means of electrolytic procedures.
The present invention also embraces using instead of copper another material which (in comparison with the aluminum material) has a reflection-enhancing effect.
In accordance with a particularly preferred embodiment it is provided that the mirror surface is cooled by the provision of a spiral copper passage or duct in the mirror cover (in which case the passage or duct is then closed by the oppositely disposed flat side of the main mirror body); typically distilled water flows through that passage or duct as the cooling fluid, wherein an advantageous spacing between the bottom of the passage or duct and the mirror surface is between 0.1 and 1 mm in order to optimise the dissipation of heat.
In accordance with a particularly preferred embodiment of the invention a cooling fluid passage or duct has a coating afforded by means of a nickel material (nickel plating). In accordance with the invention that nickel plating involves at least all inside surfaces of the fluid passage or duct, which come into contact with the cooling fluid; in a further preferred feature however the nickel plating is effected by coating the entire surface of the inward flat side of the main mirror body and, in a further preferred feature, the oppositely disposed inside surface of the mirror cover with the passages or ducts provided therein. In this respect xe2x80x98nickel materialxe2x80x99 in accordance with the invention is used to denote not only elementary nickel, but it embraces all alloys with which the advantageous effect according to the intention, namely electrochemical neutrality, can be achieved.
The use of current-less nickel has also proven to be a particularly suitable way of applying the nickel material for the nickel plating, in which respect here there are typical layer thicknesses in the range of between 10 and 100 micrometers. Current-less nickel enjoys the advantage that it can be applied in geometrically accurate manner and therefore affords in particular a uniform and homogeneous coating which can easily be produced.
While on the one hand it is particularly suitable for the mirror device which is cooled in accordance with the invention to be provided in otherwise known manner, by means of a removable adjusting plate, on the main mirror body, on or with guide units, a particularly desirable embodiment of the invention provides that the functionality of a (traditionally separate) adjusting plate is provided integrally as a component part of the main mirror body itself. That makes it possible to markedly reduce the manufacturing expenditure and accordingly the production costs without practical handling of such a unit being made more difficult, in particular upon replacement, without the need for subsequent adjustment.
Particularly with this embodiment therefore it is advantageous for the cooling device to be provided in the main mirror body itself (instead of in the mirror cover) so that as a result the mirror cover can be reduced to a thin disk or plate.
While preferred areas of use of the mirror devices according to the invention involve the wavelength region of 10.6 micrometers (corresponding to carbon dioxide lasers) and in that respect use the reflection properties of copper, which are particularly advantageous here, the present invention is not limited to that area of use but in principle is suitable for any uses which involve advantageous weight properties and/or advantageous electrochemical properties in the cooling device in conjunction with further units along a cooling line.
A particularly suitable situation of application also involves use together with otherwise known laser focusing heads, as are also produced by the applicants. In particular here it is appropriate for the mirror surface to be of an aspherical configuration, but otherwise any mirror shapes (flat, spherical or the like) can also be envisaged.